The present invention relates to a resin composition for sliding member and resin gear. More particularly, the present invention relates to a resin composition applicable for plain bearings, gears, and the like required to have a high degree of wear resistance.
In recent years, plain bearings and gears obtained by molding the resin composition are used in a large number as mechanical component parts of acoustic equipments, office appliances such as copying machines, vehicles, and other equipments. The plain bearings and gears formed of the resin composition cannot be used under a very high load and at high temperatures, unlike plain bearings and gears formed of metal. But, the plain bearings and gears formed of the resin composition are increasingly used because they are light, inexpensive, eliminates the need for using grease, and can be formed by one-piece molding.
The plain bearings and gears formed of the resin composition are required to have two characteristics that they are resistant to wear and do not attack a mating member at a high degree. That is, it is necessary that they and the mating member have a small amount of wear in their sliding contact. But the two characteristics are contradictory to each other. For example, the wear amount of gears formed of a polyphenylene sulfide resin composition is very great unless a fibrous filler is added to the resin composition. Thus, glass fiber is frequently added to the polyphenylene sulfide resin composition. But when the mating member are formed of a soft material, for example, aluminum or synthetic resin, a gear or the like formed of the resin composition attacks them at a high degree, i.e., it wears the mating member in a large amount because the glass fiber is harder than aluminum or synthetic resin. On the other hand, when a gear or the like formed of the resin composition contains a soft filler such as carbon fiber comparatively soft, it attacks the mating member in a small amount but the gear has a weak strength and are worn in a large amount.
The following resin compositions were proposed to overcome the problem, as disclosed in Laid-Open Japanese Patent Publications Nos. 5-306371 and 6-279689. The resin composition disclosed in the former comprises polyphenylene sulfide resin, polytetrafluroethylene resin, aromatic polyamide pulp, and zinc oxide whisker. The resin composition disclosed in the latter comprises synthetic resin, whisker, aromatic polyamide fiber, and solid lubricant.
In recent years, it is important to miniaturize office appliances and make the degree of noises which are generated during the operation thereof as low as possible. However, it is very difficult to form the plain bearings and gears of the conventional resin composition incapable of satisfying such demands.
The aromatic polyamide pulp and the aromatic polyamide fiber have a small apparent specific gravity, respectively and are voluminous fillers. Thus, it is necessary to granulate a resin composition and injection-mold pellet in a restricted condition, respectively. Thus, it is impossible to mold the resin composition containing the aromatic polyamide pulp or the aromatic polyamide fiber into a compact, light, and shape-complicated product.
Further, the aromatic polyamide pulp and the aromatic polyamide fiber pollute a die because they generate gas in the injection molding process. Therefore, it is necessary to clean the die repeatedly after it is used predetermined number of times, which makes it difficult to accomplish continuous molding of the resin composition containing the aromatic polyamide pulp or the aromatic polyamide fiber.
Furthermore, because the aromatic polyamide pulp and the aromatic polyamide fiber are hygroscopic, a product formed by molding the resin composition containing the aromatic polyamide pulp or the aromatic polyamide fiber may have foam formed thereon unless pellet is dried before the injection molding is performed. Further, the resin composition containing the above-described material is costly and causes the manufacturing cost to increase because of a large number of processes. Thus, plain bearings and gears formed of the resin composition containing the above-described material has a limitation in industrial application.
To prevent big noises from being generated by office appliances due to engagement of gears which are used at a fixing section or the like, of a copying machine, which are subjected to a high-load application and high temperatures, grease is applied thereto supposing that they are formed of sintered iron or the like. In this case, grease attaches to a mating gear formed of resin, thus catching resin powders and powders of fibrous reinforcing materials generated by the wear thereof. As a result, the powders act as an abrasive material on the interface between the both gears. That is, both gears are worn to a great extent. This trouble occurs outstandingly in the case where a gear is formed of a resin composition containing reinforcing glass fibers.